The present invention relates to a screen with a matrix access making it possible to represent a figure by breaking it down into a group of points or elements, whose appearance varies as a function of control signals applied to electrodes defining these elements. This screen uses a material, whose optical properties can be electrically modulated. The control signals are applied to the electrodes via non-linear resistors acting as switching elements.
The principle of the flat screen is the breaking down of said screen into M.N identical and generally square or rectangular elements, which can be individually addressed. The definition of the screen is a function of the number of points able to receive a piece of information. Thus, each point must be subject to an electrical field. This is easy to conceive in the case of a screen formed from a few dozen points. However, for high definition screens (above 1.5.10.sup.4 points) direct access using a wire to each element becomes impossible. For this reason, consideration has been given to an easily realisable matrix-type display. Each element of the screen is then defined by the intersection of two systems of orthogonal conductors called lines and columns and the number of connections passes from M.N to M+N. In the case of a high definition screen, considerable gains occur with respect to the connections.
The addressing of one element of the screen by means of control voltages applied to its line and column does not have to be maintained on adopting a time multiplexing method permitting the state of the screen to be "refreshed" or restored by recurrence. This method is based on a persistence effect, which can be physiological or available within the screen element. In the case of liquid crystal display means, the elementary cell can be likened to a capacitor, whose time constant is adequate to maintain the charge between two successive, temporary addressing operations. For applying the control voltage in a short time, a non-linear resistor is fitted in series with the capacitive cell. The non-linear resistor is a component of the varistor type having an insulating effect on this side of a voltage threshold and which becomes ever more conductive on the other side of this threshold. A convenient way of collectively obtaining the varistor elements consists of using as the substrate a block of varistor material occupying the same extension or size as the screen. However, numerous disadvantages are inherent in this process. It introduces by no means negligible stray capacitances due to the high dielectric constant of the non-linear element. In addition, as the latter is generally a varistor, which is an opaque material, the screen cannot be used in transmission.